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To focus a search, particularly when your topic contains multiple search terms.
To connect various pieces of information to find exactly what you're looking for.
Example: travel and Europe
Boolean operators form the basis of mathematical sets and database logic. They connect your seach words together to either narrow or broaden your set of results. The three basic boolean operators are: AND (narrow), OR (broaden), and NOT (exclude).
In many, but not all, databases, the AND is implied.
Google automatically puts an AND in between your search terms.
All your search terms are included in the results, although they may not be connected together in the way you want. For instance: college students test anxiety is translated to: college AND students AND test AND anxiety. The words may appear throughout the resulting records.
Phrase searches can be more helpful in some cases:
You can search using phrases by entering the quotation marks in some databases to make your results more specific.
For example: "college students" AND "test anxiety". This way, the phrases show up in the results as you expect them to be.
Use AND in a search to:
narrow your results
tell the database that ALL search terms must be present in the resulting records
example: cloning AND humans AND ethics
The purple triangle in the middle of the Venn diagram below represents the result set for this search. It is a small set using AND, the combination of all three search words.
to connect two or more similar concepts (synonyms)
to broaden your results, telling the database that ANY of your search terms can be present in the resulting records
example: cloning OR genetics OR reproduction
All three circles represent the result set for this search. It is a big set because any of those words are valid using the OR operator.
Use NOT in a search to:
exclude words from your search
example: cloning NOT sheep
it is useful if you want to narrow your search by excluding certain aspects of a topic
Databases follow commands you type in and return results based on those commands. Be aware of the logical order in which words are connected when using Boolean operators:
Databases usually recognize AND as the primary operator, and will connect concepts with AND together first.
If you use a combination of AND and OR operators in a search, enclose the words to be "ORed" together in parentheses.
Examples
ethics AND (cloning OR reproductive techniques)
(ethics OR morality) AND (bioengineering OR cloning)